Various forms of electromagnetic radiation, particularly laser light beams, have been used on skin for many years for a variety of treatments, such as hair removal, skin rejuvenation to reduce wrinkles, and the treatment of conditions such as acne, actinic keratoses, blemishes, scar tissue, discoloration, vascular lesions, acne treatment, cellulite and tattoo removal. It is well-known that some of these treatments may be performed to provide a therapeutic effect, but frequently they are all performed to provide a non-therapeutic or cosmetic effect. Most of these treatments rely on photothermolysis, where a treatment location is targeted by the treatment radiation. For example, to treat wrinkles, the dermis layer is damaged by heating (thermolysis) to induce a wound response without damage to the epidermis.
In some treatments, said heating by electromagnetic radiation takes place in the dermal layer by using radiation which can penetrate the skin as far as the dermal layer. FIG. 1 schematically shows a skin treatment device 10 known in the art, comprising a radiation source 20, and beam shaping and directing components 27. The radiation source 20 provides an incident radiation beam 22 suitable for treating human or animal skin. The radiation used may be any type of electromagnetic or thermal radiation which provides a beneficial effect in the skin. For example, when using laser light, the skin treatment device 10 may comprise a pulsed laser light source 20 such as a Nd:YAG laser with emission at 1064 nm and 1-1000 μs pulse duration.
The beam shaping and directing components 27 receive the radiation beam 22 from the radiation source 20, and create a radiation beam 22 with the desired properties which exits the device 10 along a treatment axis 21.
For example, when using laser light, these beam shaping and directing components 27 may be optical elements, such as mirrors, lenses, beam splitters, prisms etc, for directing the laser light beam 22 to exit the device along a treatment axis 21, and for focusing the light beam 22 inside the skin at a treatment location 90 on the treatment axis 21.
In a further example, if radio-frequency radiation is used, these beam shaping and directing components 27 may be waveguides, apertures, reflectors etc. for directing the radio-frequency beam 22 to exit the device along a treatment axis 21.
The skin comprises multiple layers with different radiation transmission and absorption properties. The epidermis 16 is composed of the outermost layers and forms a waterproof protective barrier. The outermost layer of the epidermis is the stratum corneum which, due to its microscopic fluctuations in roughness, impedes the coupling of radiation, in particular light, between the device 10 and the skin. Typically, a radiation coupler 12 is used between the device 10 where the radiation beam exits and the skin surface where the radiation enters into the skin. This optimizes the penetration of the treatment radiation beam 22 into the skin. For example, in the case of a laser light beam 22, an optical coupler 12 may be used which comprises lenses, mirrors, prisms, an index-matching fluid or a combination thereof. Underneath the epidermis 16, the dermis 17 is situated which is the region at which many of the skin treatments are directed.
If the device 10 is used to reduce wrinkles in the skin, the treatment location 90 is in the collagen of the dermis 17 in order to create microscopic lesions at the treatment location, which results in new collagen formation.
The laser light treatment devices 10 use the fact that the skin transmits electromagnetic radiation that is to be focused to a very small focal spot in the dermis 17. To maximize this effect, the wavelength of the laser light is between 800 and 1100 nm. In this range, transmission is high and scattering and linear absorption are low. Thus, phenomena exploited using a skin treatment, such as photothermolysis or laser induced optical breakdown (LIOB), may be achieved easily, accurately (i.e. very locally) and efficiently. It is however not excluded to use other wavelengths.
An increasing number of these non-invasive skin treatment devices are being provided for use by consumers instead of by medical professionals. Such uses are mainly for cosmetic or non-therapeutic reasons. Such home use raises new concerns, such as safety and treatment efficacy. This is particularly important when the radiation source 20 is high-powered, for example a laser.
For successful and safe skin treatments, it is crucial that the appropriate amount of energy be delivered to the treatment location 90. Delivery of too much energy results in undesirable side effects, such as scarring or burning of the skin. Delivery of too little energy results in low-efficacy treatment. Also, even under normal circumstances, reproducibility of the treatment results may vary between persons and even between anatomical regions on the same person. This is due to the inherent variability of skin properties that critically affect energy delivery efficiency.
There is thus a need for radiation skin treatment devices that are both effective and deliver reproducible results.